This invention relates to new and useful L-aspartic acid derivatives and non-toxic, pharmaceutically acceptable salts thereof and more particularly is concerned with compositions wherein such derivatives are fixed in a stable, superficially dry form usable in comestibles such as dry beverage mixes.
Synthetic sweetening agents have become quite useful in their ability to lower sugar intake and provide diets of satisfactory taste but lowered caloric value. One of the more consequential and promising sweeteners is the class of L-aspartic acid derived esters which have emerged in attempts to find new artificial sweeteners other than the more common saccharine or cyclamates which have previously been used.
The use of such recent sweeteners in comestibles and particularly in dry mixes such as in beverage mixes presents a significant opportunity to provide sweetness equivalent to sucrose. However, it is important that the esters be stabilized in a form whereby they do not undergo degradation with accompanying loss of sweetness and are unavailable for reaction with aldehydes or ketones or other agents which may alter intended organoleptic response when the ultimate sweetened composition is consumed. Many of these L-aspartic acid derivatives such as L-aspartyl-L-phenylalanine methyl ester (APM) are prone to undergo a loss of sweetness in the presence of moisture rendering such derivatives virtually non-functional in many food applications. Moreover, in attempts to stabilize the ester in a dry fixation, it is important that it be uniformly distributed to provide sweetness uniformity; this is quite important in view of the manifold sweetening power of such esters. A related requisite is that any fixed ester be stable against caking; many such esters are per se prone to cluster and even when fixed in certain matrices will promote such caking as occasions the need for expensive packaging barriers; even under the most extreme moisture protection common fixation of esters such as APM can experience caking due to the character of the ester and its capacity to gain moisture with increasing relative humidities, particularly when stored with other food materials such as food acids like citric acid and colloids such as hygroscopic dextrins.
It is desirable, therefore, to so compose the L-aspartic acid derivatives in a form whereby they do not suffer the foregoing sensitivities to storage conditions. Preferably such a composition should have a reasonably controlled equilibrium relative humidity, that is an equilibrium relative humidity wherein it does not significantly absorb moisture to an extent whereby the derivative undergoes decomposition or reaction. The high order of sweetness necessitates use of the compounds in controlled amounts as a minor weight constituent of the total powderous mixture of which they form a part, typically less than 15%. In order to facilitate handling of the sweetening compositions of which the ester is a part, it becomes desirable to have the derivative compound fixed in a suitable solid carrier at a very high weight percent, generally in excess of 20% of the carrier or fixative. It is desirable to minimize the amount of fixative for the sweetening derivative since it is otherwise non-functional, adds bulk and cost, and indeed detracts significantly from the ability to market comestibles with claims for substantial reduction of calories. It also becomes quite desirable to have the carrier associated with the L-aspartic acid derivative by a process which does not significantly reduce the density of the sweetening ester-containing composition particles; this reduces any segregation difficulty encountered by reason of too wide a disparity with food acid or like particles having a high bulk density, say, of about 0.8 grams per cc. The absolute density of one of these L-aspartic acid derivatives (APM) is in an order of 1.038 grams per cc. but the bulk density of its characteristic needle-like crystalline structure is about 0.2 grams per cc; thus, it becomes desirable to achieve a density in the composition containing the derivative as high as practicable and in any event not less than 0.2 grams per cc. to provide flow and handling properties facilitating uniformity in mixing and packaging of the synthetic sweetening agent in powderous beverage and like mixes for other comestibles having significant amounts of higher density particles. Concomitantly, in effecting this density criteria, it is important that the carrier provide the foregoing protection against other packaging conditions which are set forth hereinabove; i.e. the effects of moisture as by providing a relatively low-hygroscopic state. Furthermore, it becomes desirable to achieve both objectives of bulk density increase and a compatible equilibrium relative humidity uniformly in a composition that can be economically processed without a significant loss of the L-aspartic acid ester derivative in functionaity or yield as by premature or uncontrolled crystallization and interference or interruption of the fixation operation, as by spray drying or loss of sweetness and flowability in mixes upon storage. Indeed, it is most preferred to employ a process which minimizes the hazard of functionality loss by high temperature processing such as may be required to render soluble and/or uniformly distributed the comparatively insoluble sweetening dipeptide.